Radio receiving system



Feb-2s, 19%. Y @OCARD Emlyn RADIO RECEIVING SYSTEM Filed Jan. 15, 1952YVES ROCARD I NVENTOR ATTURNEYS Patented Feb. 25, 19 36 UNITED STATES2,031,736 RADIO RECEIVING SYSTEM Yves Rocard, Paris, France, assignor toLa Radiotechnique, Paris, France, a corporation of France ApplicationJanuary 15, 1932, Serial No. 586,768

. In France January 22, 1931 l v 5 Claims. (01. 250 -20) sirable,namely, the tuned circuit is placed in This invention relates to aradio-receiving apparatus having frequency change characteristics and aseparate oscillator and the invention renders possible the regulationsof the circuit tuned to the frequency received and of the heterodynecircuit totally independent of one another in a frequency changingsystem, as for example, in a superheterodyne radiotelephonic receiver.The invention may be carried out by various means of which anonrestrictive example will be given. The principal effect obtained bythe invention is the elimination of the blank spots which thesereceivers always present in the range of received frequencies, and theinvention makes it possible for the single control of the tunings of thecircuits to be effected in a simple and practical manner.

In the case of a superheterodyne receiver embodying a separateoscillator, it will be appreciated that there exists a coupling betweenthe circuit tuned to the frequency to be received, and that traversed bythe frequency of the heterodyne, and in particular by the parts whichconduct the two frequency currents into the tube which is arranged toeffect the detection of the intermediate frequency. For example thistube will have its grid connected to a circuit tuned to the frequency ofthe wave to be received, and the impedance of this tuned circuit will becoupled to a coil forming a part of the circuit tuned to the heterodyne;and such a coupling is sufficient to make the regulations of the tunedcircuit and of the heterodyne interdependent, and to prohibit the1possibility of employing a strictly single contro As a matter of fact,the input circuit of the control grid of the tube which is arranged todetect the mean or intermediate frequency, is generally tuned by acondenser. This resonant circuit is thus shunted by the capacitiesformed between the control grid and the cathode and between the controlgrid and the plate of the tube, each being in series with the impedancein the circuit of the corresponding electrode. It will be understoodthat if this grid-cathode or grid-plate capacity comes intoresonance-series with the charge impedance in question (which will befor example the oscillating circuit of the heterodyne), the aforesaidinput circuit will be shunted by a resulting zero impedance; at thefrequency for which this is produced there will be no signal impressedupon the grid, and the receiver will have a blank spot at thisparticular wave frequency. If recourse is taken to changing the beat bymanipulating the heterodyne, this effect may be avoided, but there isthen produced an effect which is quite as underesonance-series by thecapacity existing between the grid and the other electrodes andshort-circuits the oscillating circuit of the heterodyne.

Now with the inherent capacities between electrodes which are present inthe tubes, with the order of the mean frequencies employed, thesephenomena are produced actually in the scale of broadcast frequenciesand they are only avoided by using the second or third harmonic of theheterodyne, a procedure which cannot usually be employed over the wholescale without inconveniences, as the fundamental of the heterodyne willsometimes, be very close to the mean frequency, and, furthermore, theamplitude of the harmonics in question varies considerably over. thescale of frequencies. 7

In addition to the serious disadvantages above described, thisinterdependence or mutual reactionof the circuits always introduces amutual dependence of the regulations of the two circuits, whichundesirable coupling. by its tendency to capricious variation over thescale of frequencies and variation from one tube to another, makes theemployment of a single control practically impossible. In otherwords,with the undesirable coupling present between circuits of differentfrequency as in'the case of known superheterodyne receivingcircuits,when two aligned condensers are adjusted to their most favorableposition for a predetermined frequency, if then the two condensers aresimultaneously turned in order to obtain another frequency, it would bepossible to obtain the most favorable position of only one of thesecondensers, for the second condenser could not be properly set by thesame control, even if it varies in accordance with the same law as inthe case of the former condenser. This divergence will vary: to thegreatest extent if the tube involved'is replaced by another one ofslightly different characteristics. j

:The present invention makes the regulations of thecircuits. tuned tothewave to be received independent of the regulation of theheterodyne,

, and conversely. By this, it is meant that the position of the variablemember (for example, a variable condenser) which tunes the receivingcircuit to a carrier wave, is independent whatever may be the valuegiven to the frequency of the heterodyne. It is established that thetunings to the carrier wave and the heterodyne follow simple and.regular laws as a function of the capacities, for example, -variable,which renders it possible for a single control tobeemployed.

1 and 3 represent superheterodyne circuits. era--- ploying a separateoscillator and arranged in accordance with the invention, and Figure 2illustrates a modified circuit detail applicable to each of the circuitsillustrated in Figures Land 3.

The essence of the invention consists in conducting the two oscillatorycurrents, namely, that of the receiving circuit and that of theheterodyne.

to the grid of the tube of a superheterodyne receiver which produces theintermediate frequency, by means which, from all practicalconsideration, produce no coupling between the two tuned circuits. As anexample of means which attain this result there is provided a highresistance potentiometer, for example of 250,000 ohms, of which the twoextremities are connected one to the output of the circuit tuned to thewave to be received, and the other to the output of the circuit of theheterodyne, or to a point of oscillating potential of this circuit. Theintermediate point of the potentiometer is connected to the grid of thetube producing the intermediate frequency so that, for example, 50,000ohms of the potentiometer are located on the side of the circuit tunedto the wave to be received and 200,000 ohms thereof on the side of theheterodyne.

This arrangement is primarily illustrated in Figure l in which an aerialI is connected through a small capacity C0 to a tuning circuit L101connected to the grid of a screened grid high frequency amplifying tube2. In the plate circuit of the tube 2 a shock impedance ch is inserted,and a large capacity C'o is arranged in'shunt to feed a tuning circuitL202. This latter circuit is connected through a resistance T which maybe of, for example, 50,000 ohms to the grid of the tube 3 producing theintermediate frequency and which is followed by an intermediatefrequency filter 5. The oscillating circuit C3L of an oscillating tube 4is connected to the grid .of the tube although other arrangements arepossible, and is also connected to the grid of the tube 3 through aresistance R, the value of which is, for example, 200,000 ohms.

The operation of the apparatus is as follows:

Let Z be the impedance of the circuit L: C: for the frequency of theheterodyne. At the terminals of the circuit L3 C3, an oscillation of 20volts will generally be produced, of which the fraction:

will alone be transmitted to the grid of the tube 3. This fractionamounts to about 4 volts which is amply sufiicient for the tube 3 togive a good detection by means of the plate. On the other hand, if Z1 bethe impedance offered by the cir-r cuit L3 C3 and its couplings for thefrequency of of the volts of the heterodyne.

the wave received, it will be represented by the fraction:

1 r+ R+Z of the volts at the terminals of the circuit L2 C2 which willbe transmitted to the grid of the tube 3. With the values of r and Rabove indicated, this fraction will be of the order of about which meansthat this method of coupling will only have caused the loss of fl th ofthe amplification. It will furthermore be appreciated that as the twocircuits L2 C2, L3 C3 are only connected through the high resistancer-i-R, this high resistance coupling does not introduce any reciprocaldependence between the regulations of the two circuits and the object ofthe invention is thus fully attained by the described arrangement.

In regard to the selection of the proper values for the resistances rand. R, it is advisable to make 1' and R as large as possible whilst R/rremains large. But this is not exact on account of the existence of acertain capacity C between the grid of the tube 3 and earth and whichwill ordinarily be of the order of 10 cm. If it is desired that thearrangement described should act correctly without too much loss ofamplification of the signal wave received, it is at least necessary that1' remains small as compared with the leakage impedance offered by thecapacity C, ar representing the cycles.

As this impedance is particularly small when w, representing thefrequency, increases, that is to-say, with short waves, the inventionprovides that the resistances r and R may be variable, or more simply,that the total resistance r+R is constituted by a potentiometer, thevariable point of which is connected to the grid of the tube 3, and inthis way r and R may be best adjusted, and in particular 1' be madeequal to zero for short wave reception, in which case the whole of thevoltage of the received frequency would be delivered to the grid of thetube 3 and only the fraction This naturally requires that Z shall befairly large, which is the case for the range of wave lengths of 200meters-600 meters, and a mean frequency of the order of 60,000 cycles.On the contrary, with a range of wave lengths of from 1000 meters to2000 meters Z would equal 2000 ohms only, with the usual values of theimpedances and tuning capacities, in which case the long waves, thepassage from one to theother being effected by means of a selectorswitch as shown in Figure 2.

It will also be appreciated that the manipulation of the potentiometerabove mentioned, also constitutes a volume control, but this volumecontrol nevertheless does not render it possible for the intensity to bereduced absolutely to zero. It may be completed by introducing in shuntbetween the grid of the tube 3 and earth, a variable resistance R1, asshown in Figure 3, which may be reduced to zero and of which the maximumvalues should be very high, of the order of 10 ohms, so as not todiminish the efficiency of the arrangement when it is necessary that itshould possess a maximum sensitiveness.

What I claim is:

1. In a radio receiver of the heterodyne type, the combination of acircuit arranged to be traversed by the radio frequency currentsreceived and having a terminal subjected to a predetermined radiofrequency potential with respect to the earth, a generator ofoscillations of inaudible frequency having an output circuit, aconnection comprising a high ohmic resistance between the output circuitof the said generator and said terminal of the said first-named circuit,a tube having a plurality of electrodes, one of which is an inputelectrode and a conductive connection between the input electrode of thesaid tube and an intermediate point on the said resistance.

2. In a radio receiver of the heterodyne type, the combination of acircuit arranged to be traversed by the radio frequency currentsreceived and having a terminal subjected to a predetermined radiofrequency potential with respect to the earth, a generator ofoscillations of inaudible frequency having an output circuit, aconnection comprising a high ohmic resistance between the output circuitof the generator and said terminal of the said first-named circuit, atube having a plurality of electrodes, one of which is an inputelectrode, a conductive connection between the input electrode of thesaid tube and an intermediate point on the said resistance and meansoperable to vary the position of the said point between the ends of theresistance.

3. In a radio receiver of the heterodyne type, the combination of acircuit arranged to be traversed by the radio frequency currentsreceived and having a terminal subjected to a predetermined radiofrequency potential with respect to the earth, a generator ofoscillations of inaudible frequency having an output circuit, aconnection comprising a high ohmic resistance between the output circuitof the said generator and said terminal of the said first-named circuit,a tube having a plurality of electrodes including a control grid, one ofwhich is an input electrode and a conductive connection between the saidgrid and an intermediate point on the said resistance.

4. In a radio receiver of the heterodyne type, the combination of acircuit arranged to be traversed by the radio frequency currentsreceived and having a terminal subjected to a predetermined radiofrequency potential with respect to the earth, a generator ofoscillations of inaudible frequency having an output circuit, aconnection comprising a high ohmic resistance between the output circuitof the said generator and said terminal of the said first-named circuit,a tube having a plurality of electrodes including a control grid, one ofwhich electrodes is an input electrode, a conductive connection betweenthe said grid and an intermediate point on the said resistance, and avariable ohmic resistance interposed between the said point and earth.

5. In a radio receiver of the heterodyne type, the combination, with atube having a plurality of electrodes, one of which electrodes is aninput electrode, of an input circuit connected to the control grid ofsaid tube and arranged to be traversed by the radio frequency currentsreceived by said receiver, an oscillation generator having an outputcircuit and being connected to the connection between the input circuitand the control grid of the said tube in order to produce a differentfrequency in the output circuit of said tube, an ohmic resistanceinserted in the connection between the output circuit of the oscillationgenerator and the control grid of the said tube, and a second ohmicresistance interposed between the output of the said input circuit and apoint of the first mentioned ohmic resistance connected to the controlgrid of said tube.

YVES ROCARD.

